So called “fat pads” exist on the epicardial surface and are regions often associated with autonomous activity. Various patents discuss stimulation of fat pads to affect the heart. For example, U.S. Pat. No. 5,507,784, entitled “Method and apparatus for control of A-V interval,” to Hill and Mehra, issued Apr. 16, 1999 ('784 patent), discusses stimulation of fat pads associated with the SA and AV nodes. In particular, the '784 patent states that the “fat pad associated with the SA node . . . is located along the anterior AV groove in most humans” and that the “fat pad associated with the AV node . . . is located along the posterior AV groove in most humans.” U.S. Pat. No. 6,266,564, entitled “Method and device for electronically controlling the beating of a heart,” to Hill and Jonkman, issued Jul. 24, 2001 ('564 patent), also discusses “fat pad” stimulation. In particular, the '564 patent references a study entitled “Selective Stimulation of Parasympathetic Nerve Fibers to the Human Sinoatrial Node,” Circulation, 85(4): 1311-1317 (1992), which reported that “cardiac parasympathetic nerve fibers located in an epicardial fat pad at the margin of the right atrium, the superior vena cava, and the right pulmonary vein in humans could be electrically stimulated to affect the heart rate.” However, as discussed herein, a more recent study by Pauza et al., “Morphology, distribution, and variability of the epicardiac neural ganglionated subplexuses in the human heart,” The Anatomical Record 259(4): 353-382 (2000), demonstrates that significant populations of autonomic nerves exist in other epicardial locations.
The aforementioned '784 patent also discusses a lead to stimulate the AV nodal “fat pad” wherein the lead has two electrodes located within the coronary sinus, adjacent the ostium. Further the '784 patent states that “AV nodal fat pad stimulation may also be accomplished by means of one electrode located adjacent the ostium of the coronary sinus and a second electrode located in the inferior vena cava, by means of electrodes located in the left atrium or by means of epicardial electrodes applied on or adjacent the AV nodal fat pad.” However, the '784 patent does not disclose any epicardial electrodes or leads having epicardial electrodes. While the aforementioned '564 patent discusses electrodes for stimulation of “fat pads,” such stimulation is limited to electrodes located on transvenous leads located in veins adjacent nerve fibers to be stimulated. Given the relationship between fat pad stimulation and cardiac function, a need exists for alternative or improved stimulation techniques. In particular, a need exists for epicardially positionable leads that can stimulate a variety of autonomic nerves or other cardiac tissue.